1. Field of the Invention:
The present invention relates to a submergible motor pump which is mainly used for construction work, the pump having a vortex impeller attached to an end of a motor shaft. More specifically, the present invention relates to a submergible motor pump having a relatively wide gap in front of the impeller, thereby enabling foreign substances, for example, sands, to be discharged, together with a vortex generated in the space defined by the wide gap when the pump is operated.
2. Prior Art:
A conventional submergible motor pump which is mainly used for construction work is arranged as shown in FIG. 1. A semiopen impeller 1 which has no forward shroud but only a main shroud at the back side is attached to an end portion of a motor shaft 3 and accommodated in a pump casing 5 comprising an intermediate casing member (bracket) and a lower casing member, which are formed together in an integral structure, and a suction cover 7 is mounted at the suction side with a minute gap S.sub.1 (1 to 2 mm) provided between the same and the forward end face of the impeller 1. A bottom plate 11' is mounted by means of a bolt 13' below the suction cover 7 through a cylindrical strainer 9'. In the figure, reference numerals 15 and 17 denote a mechanical seal and a lubricating oil, respectively.
In operation, a fluid that is sucked in through the strainer 9' in response to the rotation of the impeller 1 is raised in pressure by the action of the impeller 1 and discharged to the outside through a flow passage 19.
The conventional submergible motor pump described above, however, involves the following problems:
(i) It is necessary to precisely adjust the minute gap S.sub.1 for the impeller 1, making maintenance difficult and time consuming. PA0 (ii) To form the flow passage 19 inside the pump casing 5, a core 19a is needed for the casting process, as shown in FIG. 2(b). In addition, as shown in FIG. 2(a), a large number of portions (indicated by the mark .gradient. in the figure) require machining. Accordingly, a great deal of labor is required for shaping and machining operations. PA0 (iii) It has heretofore been impossible to produce the pump casing 5 using a wear-resistant material, for example, an elastomeric material, from the configurational point of view. PA0 (iv) Since the impeller 1 is installed in the inner part of the pump casing 5, it is difficult to remove the impeller 1 for replacement even if the suction cover 7 is removed, as shown in FIG. 3, and a special jig must be employed to remove the impeller 1. PA0 (v) To replace the pump casing 5 which has become worn, the mechanical seal 15, even if it is in good condition, must be removed. PA0 (vi) It is also necessary to discard the lubricating oil 17 when the pump casing 5 is replaced.